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Project Progress

Graduate Student Jennifer Glass has recently written a hypothesis paper (in prep. for Nature Geoscience) in collaboration with Eric Boyd (MSU Team), Steve Romaniello and Ariel Anbar on an idea she first presented at a 2010 AbSciCon Lightning Talk, which is summarized here: In modern biological systems, molybdenum (Mo)-nitrogenase is the primary enzyme responsible for the conversion of dinitrogen to ammonia. However, in the low-Mo Archean ocean, it is thought that nitrogen fixation was catalyzed by nitrogenase enzymes that contained vanadium (V) or iron (Fe) in place of Mo. During dinitrogen reduction these “alternative” forms of nitrogenase expend significant energy in the form of hydrogen gas, resulting in the need for an additional ~8 (V-nitrogenase) and ~32 (Fe-nitrogenase) mol ATP per catalytic cycle when compared to Mo-nitrogenase. A fraction of this energy can be recovered if the hydrogen produced by nitrogenase is recycled by Ni-Fe hydrogenases. We propose that a drop in marine Ni concentrations 2.7 billion years ago (Konhauser et al., 2009, Nature) may have impaired the activity of these hydrogenase enzymes, leading to a reduced ability of organisms to recycle the hydrogen produced by alternative nitrogenases. In combination with transient pulses of Mo into the ocean as a result of increased oxidative weathering during this period, this marine Ni famine could have provided the evolutionary impetus for the evolution of the more efficient Mo-containing form of nitrogenase.